Source: lib/util/lazy.js

  1. /*! @license
  2.  * Shaka Player
  3.  * Copyright 2016 Google LLC
  4.  * SPDX-License-Identifier: Apache-2.0
  5.  */
  7. goog.provide('shaka.util.Lazy');
  9. goog.require('goog.asserts');
  12. /**
  13.  * @summary
  14.  * This contains a single value that is lazily generated when it is first
  15.  * requested.  This can store any value except "undefined".
  16.  *
  17.  * @template T
  18.  */
  19. shaka.util.Lazy = class {
  20.   /** @param {function():T} gen */
  21.   constructor(gen) {
  22.     /** @private {function():T} */
  23.     this.gen_ = gen;
  25.     /** @private {T|undefined} */
  26.     this.value_ = undefined;
  27.   }
  29.   /** @return {T} */
  30.   value() {
  31.     if (this.value_ == undefined) {
  32.       // Compiler complains about unknown fields without this cast.
  33.       this.value_ = /** @type {*} */ (this.gen_());
  34.       goog.asserts.assert(
  35.           this.value_ != undefined, 'Unable to create lazy value');
  36.     }
  37.     return this.value_;
  38.   }
  40.   /** Resets the value of the lazy function, so it has to be remade. */
  41.   reset() {
  42.     this.value_ = undefined;
  43.   }
  44. };